Reinforced polyamides are playing an increasing role in the field of technical construction materials, since they have high rigidity, high toughness and high heat distortion temperature. Fields of application are, for example, internal and external parts in the automotive sector and in the field of other means of transport, housing material for appliances and equipment for telecommunication, consumer electronics, household appliances, machinery equipment, apparatus in the field of heating and fixing parts for installation. Metal like properties are important for parts, for example, in the automotive sector, but these can only be achieved by highly filled, reinforced molding materials. For thin-walled parts, particularly a high flow length of the molding materials is necessary, which flow length, however cannot or can only very poorly be achieved in molding materials that are reinforced by endless fibers.
There is also a special advantage of reinforced polyamides in the exceptionally good bonding between polymer matrix and reinforcing materials. This is true even at high reinforcement levels, resulting in products with high tensile modulus of elasticity. However, the toughness of the products is not sufficient to fulfil all requirements.
Polymers which are regarded as polyamides in the present invention that have basic building blocks, which are held together by amide bonds (—NH—CO—), and which can be prepared by polycondensation or polymerization of monomers, as for example dicarboxylic acids, dicarboxylic acid halides, dinitriles, diamines, aminocarboxylic acids and/or lactames. They can be homopolyamides or copolyamides. The average molecular weight of the polyamide should be more than 5,000, preferably more than 10,000 but less than 20,000, corresponding to solution viscosities of ηrel lower than 1.9, especially ηrel lower than 1.8, particularly preferred ηrel lower than 1.7.
EP 0 190 011 B1 describes glass fibers with elliptical or rectangular cross-section, as well as their manufacture. The use of these particular glass fibers for the manufacture of composite parts is mentioned. Due to the larger surface of the fibers, higher strength values result in the composites.
EP 0 196 194 B1 describes a strand consisting of a variety of glass monofilaments with a non-circular cross-section, as well as their manufacture. The cross-section of the glass fibers can be oval, elliptical, cocoon shaped or polygonal.
EP 0 199 328 B1 describes a fabric for printed circuit boards, which is essentially made of glass fibers with non-circular cross-section. The individual fibers have oval, elongated or elliptical cross sections. Unsaturated polyester resins, epoxy resins, phenol resins, polyimide resins or PTFE are described as matrices for this fabric.
EP 0 246 620 B1 describes an article made of a glass fiber reinforced thermoplastic resin. The, glass fibers have a rectangular, elliptical or cocoon shaped cross section. It is shown that glass fibers with non-circular cross-section have advantages in terms of strength and toughness, especially at a high degree of reinforcement (≧60%).
EP 0 376 616 B1 describes a thermoplastic polymer composition comprising a thermoplastic resin and 1 to 65% of a fibre like reinforcement with a non-circular cross-section, wherein the cross-sectional area and the ratio of the perpendicular cross-sections of the reinforcing fibers are characterized in more detail. The cross-section of the reinforcing fibers has a semicircular or arcuate contour. The composition is characterized by high dimensional stability and reduced warpage.
EP 0 400 935 B1 describes a flame retardant fiber reinforced polyester composition that includes 1 to 60 wt % glass fibers. According to EP 0 400 935 B1, the used glass fibers have a cross-sectional shape, which is selected from the group of flattened, elliptical, oval, partly circular, curved and rectangular cross-sectional shapes. These flame retardant reinforced polyester composites according to EP 0 400 935 B1 show a decreased deformation without their mechanical properties being adversely influenced by crystalline polyester resins. In this respect, it was found according to EP 0 400 935 B1 that the deformation, i.e. warping of crystalline polyester resins can be reduced without reducing the mechanical properties of the resin, for example, the bending strength and rigidity and the processability.
According to JP 10219026 A2 the thermoplastic matrix is reinforced by a mixture of glass fibers with a circular cross-section and glass fibers with a flat cross section to reduce warpage of thermoplastic parts. Polyamide 66 is used as a polymer matrix in the only example of this document.
JP 2004285487 A1 describes a bundle of glass fibers, consisting of glass filaments with a flat cross-section, which are hold together by a non-volatile sizing, and a thermoplastic composition, consisting of 5 to 75% of glass fiber bundles and a polyolefin matrix.
JP 2006045390 A2 describes a granulate reinforced by long glass fibers, consisting of a thermoplastic matrix and up to 60 wt.-% of glass fibers with a flat cross section. Granulate length and fiber length is identical. Advantageous features of molded parts made from the reinforced composition according to JP 2006045390 A2 are good surface quality and high impact strength.
Polyamide molding materials, which have good mechanical properties and a very small warpage, are described in the still unpublished patent application EP 06014372.4. These properties are obtained by a combination of transparent polyamide with fibrous reinforcing materials and particulate fillers. Regarding the fibrous reinforcement materials there are basically no restrictions. They are preferably selected from the group consisting of glass fibers, carbon fibers, metal fibers, aramide fibers, whiskers and mixtures thereof. The glass fibers can be added as endless fibers or as chopped glass fibers. The glass fibers can have round, oval or rectangular cross section.
The also still unpublished application EP 05025216.2 describes reinforced polyamide molding materials made from a blend of polyamide 66 and a copolyamide 6T/6I. A mixture of glass fibers and carbon fibers is used as a reinforcing material. To further increase the rigidity, a portion of the glass fibers is substituted by carbon fibers, so that a hybrid fiber reinforced compound is used.